Blueshifted hydrogen emission and shock wave of RR Lyrae variables in SDSS and LAMOST

TL;DR

This study develops a pattern recognition algorithm to identify blueshifted hydrogen emission in RR Lyrae stars from SDSS and LAMOST spectra, discovering 127 such stars and analyzing their properties, including a detailed case of a Blazhko type star.

Contribution

The paper introduces a novel pattern recognition method applied to large spectroscopic surveys, significantly expanding the database of hydrogen emission features in RR Lyrae stars.

Findings

Identified 127 RR Lyrae stars with blueshifted hydrogen emission.

Largest database to date of hydrogen emission in RR Lyrae variables.

Characterized a Blazhko type RR Lyrae star with long-term emission modulations.

Abstract

Hydrogen emissions of RR Lyrae variables are the imprints of shock waves traveling through their atmospheres. We develop a pattern recognition algorithm, which is then applied to single-epoch spectra of SDSS and LAMOST. These two spectroscopic surveys covered $\sim$ 10,000 photometrically confirmed RR Lyrae stars. We discovered in total 127 RR Lyrae stars with blueshifted Balmer emission feature, including 103 fundamental mode (RRab), 20 first-overtone (RRc), 3 double-mode (RRd), and 1 Blazhko type (temporary classification for RR Lyrae stars with strong Blazhko modulation in Catalina sky survey that cannot be characterized) RR Lyrae variable. This forms the largest database to date of the properties of hydrogen emission in RR Lyrae variables. Based on ZTF DR5, we carried out a detailed light-curve analysis for the Blazhko type RR Lyrae star with hydrogen emission of long-term modulations. We characterize the Blazhko type RR Lyrae star as an RRab and point out a possible Blazhko period. Finally, we set up simulations on mock spectra to test the performance of our algorithm and on the real observational strategy to investigate the occurrence of the "first apparition".